Evaluation of radiation exposure risk from 90Y in the light of internal bremsstrahlung emission

Purpose: Internal bremsstrahlung (IB), occurring after interaction of electrons with the parent nuclide, is usually neglected when estimating absorbed dose from exposure to  emitters. Nevertheless, for a set of high energy radionuclides some Authors pointed out that IB emission intensity can be comparable to (or somehow larger than) the external bremsstrahlung (EB). By means of Monte Carlo (MC) simulations and experimental measurements for 90 Y, we studied the relevance of IB contribution to the total absorbed dose to the extremities of operators handling real sources. Materials and Methods: Given the great variety of IB models existing in literature, and basing on the available experimental data, we assumed two different hypotheses for IB spectrum and implemented both of them in MC simulations, in order to estimate skin and deep absorbed doses for point-like and extended 90 Y sources (glass and plastic vials). Dose measurements were performed in different configurations, using a pure 90 Y liquid source in a glass vial and two portable radiation monitors, calibrated in H*(10). Results: Evaluation of absorbed doses due to  particles, and consequently to the EB x-rays, was already carried out in a previous work of ours, using GAMOS, for the same geometrical configurations. Keeping into account also IB contribution, we now get increased absorbed doses; depending on the adopted model of IB spectrum, increments respectively up to 34% and 60% or 15% and 28%, for a point source and the considered receptacles, are obtained. Conclusions: This study indicates that IB phenomenon accompanying -decay can induce relevant contribution in radiation protection estimations and suggests to extend future theoretical and experimental studies to other  decaying radionuclides. Keywords: Internal bremsstrahlung; external exposure; yttrium-90; Monte Carlo.